1. Field of the Invention
This device relates to an improved latch for securing together two members and more particularly, but not by way of limitation, to a latch for securing together a pair of hinged cowlings or ducts of an aircraft nacelle
2. Background Information
Modern jet engines commonly include a pair of thrust reverser ducts or cowls that, during aircraft operation, define the outer walls of the engine exhaust nozzle. Such thrust reverser ducts must be capable of withstanding considerable loads caused by the high pressure of the jet exhaust stream, which it contains. The thrust reverser ducts are normally hingedly connected to the upper portion of the nacelle near the point where the nacelle is attached to the engine support strut. The ducts can be pivoted upwards about their hinge points to provide access to the engine for maintenance and repair. For aircraft operation, the ducts are pivoted downwards into closed positions in which their lower ends are adjacent to one another, or adjacent to an interposed strut, services channel or bifurcation. The closed ducts are then secured by latches to form a continuous circumferential load bearing structure.
The design of latches for thrust reverser ducts is complicated by a number of factors. For example, thrust reverser ducts must have an appreciable thickness to accommodate flow reversing cascades, and the inner surfaces of the ducts must include a load bearing member or ring to withstand the aforementioned loads due to internal pressure. Furthermore, a large circumferential force must be applied during latching to ensure satisfactory flange seating.
Prior to the latch of this invention, existing latches were standard over center latches with a sliding hook arm and a folding handle. The entire take-up was accomplished in a single closing stroke followed by a folding stroke which was used solely to secure and stow the handle. The existing latches have had to compromise between the handle force necessary to close the latch and the length of the take-up stroke. For instance, the need has been to have a latch wherein typically fifty pounds (50 lbs.) of handle operating force would allow for a take-up of typically two and a half inches (2.5 inches) within a limited operating envelope that limits handle size. The problem has traditionally been resolved by allowing increased handle operating force or reduced take-up stroke. In some instances, a force of one hundred thirty pounds (130 lbs.) was required. The existing latch does not accomplish any work during handle folding, so all of the take-up must be accomplished in a single take-up stroke.